Structural basis for differential binding of the interleukin-8 monomer and dimer to the CXCR1 N-domain: role of coupled interactions and dynamics.
Structural basis for differential binding of the interleukin-8 monomer and dimer to the CXCR1 N-domain: role of coupled interactions and dynamics.
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DOI：
10.1021/bi901194p
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发表时间：
2009-09-22
期刊：
影响因子：
2.9
通讯作者：
Rajarathnam, Krishna
中科院分区：
文献类型：
--
作者：
Ravindran, Aishwarya;Joseph, Prem Raj B.;Rajarathnam, Krishna
白细胞介素-8（IL-8或CXCL 8）通过结合和激活属于GPCR类的受体CXCR 1，在协调免疫应答中发挥关键作用。IL-8以单体和二聚体的形式存在，两者都结合CXCR 1，但亲和力不同。已充分确定单体是高亲和力配体，并且配体N-环和受体N-结构域之间的相互作用在确定结合亲和力中起关键作用。为了表征IL-8单体和二聚体与CXCR 1 N结构域的差异结合的结构基础，我们分析了结合诱导的NMR化学位移和峰强度变化，并表明它们非常敏感，可以提供详细的结合过程。我们使用了三种IL-8变体，一种设计的单体，一种捕获的二硫键连接的二聚体，以及二聚体浓度的WT。单体的NMR数据显示，跨越整个N-环的非连续残基参与结合过程，并且结合是由广泛的直接和间接偶联相互作用的网络介导的。有趣的是，在WT的情况下，结合诱导二聚体-受体复合物解离为单体-受体复合物，并且在捕获的二聚体的情况下，结合导致全局构象灵活性增加。增加的动力学是不利相互作用的证据，表明WT二聚体的结合触发破坏二聚体-界面相互作用的构象变化，导致其解离。这些结果共同提供证据表明，结合不是一个本地化的事件，但在单体内和整个二聚体界面的广泛耦合的相互作用的结果，这些相互作用在确定结合亲和力发挥了重要作用。
Interleukin-8 (IL-8 or CXCL8) plays a critical role in orchestrating the immune response by binding and activating the receptor CXCR1 that belongs to the GPCR class. IL-8 exists as both monomers and dimers, and both bind CXCR1 but with differential affinities. It is well established that the monomer is the high-affinity ligand and that the interactions between the ligand N-loop and receptor N-domain play a critical role in determining binding affinity. In order to characterize the structural basis of differential binding of the IL-8 monomer and dimer to the CXCR1 N-domain, we analyzed binding-induced NMR chemical shift and peak intensity changes and show that they are exquisitely sensitive and can provide detailed insights into the binding process. We used three IL-8 variants, a designed monomer, a trapped disulfide-linked dimer, and WT at dimeric concentrations. NMR data for the monomer show that nonsequential residues that span the entire N-loop are involved in the binding process and that the binding is mediated by a network of extensive direct and indirect coupled interactions. Interestingly, in the case of WT, binding induces dissociation of the dimer–receptor complex to the monomer-receptor complex, and in the case of the trapped dimer, binding results in increased global conformational flexibility. Increased dynamics is evidence of unfavorable interactions, indicating that binding of the WT dimer triggers conformational changes that disrupt dimer–interface interactions, resulting in its dissociation. These results together provide evidence that binding is not a localized event but results in extensive coupled interactions within the monomer and across the dimer interface and that these interactions play a fundamental role in determining binding affinity.
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